The present invention relates to linerless closures for containers. More particularly, the invention relates to such closures for use in hot fill and aseptic processes.
Refrigeration or preservatives are two techniques that have long been used for ensuring that foods and beverages remain suitable for consumption by consumers. Canning, where products are heated in the container over a period of time, has also long been used as a means of sterilising food products.
Hot fill and aseptic processing are two more recent techniques developed for sterilising foods and beverages. Hot fill processing is used in the packaging of beverages such as iced tea, water and fruit juice. Aseptic processing is also used in the packaging of these products and other foods including milk, soups, yoghurts and tomato products.
In the hot fill process, the containers are filled with the beverage while the beverage is still hot. This process serves to sterilise the beverage before sealing of the container. Beverages packed in this way can be shipped without the need to provide refrigeration of the containers.
Due to the temperatures involved, the hot fill process results in an expansion of the container and closure subsequent to the filling and sealing of the container. The subsequent cooling of the container typically extends over a considerable period and creates a partial vacuum inside the container due to contraction of the beverage and of the air in the void above the beverage.
Closures for sealing containers filled using the hot fill process must be able to withstand the high temperatures of the filling process and remain sealed to the container during cooling of the container after filling. Closures for hot fill application usually comprise a polypropylene cap having a top and depending skirt, with a wad or liner positioned within the cap and fixed to the underside of the top.
Linerless closures have also been proposed for use in hot fill applications. Typically, such linerless closures rely on a bore seal that extends into the bore of the end portion of the container and seals with the inside surface of the end portion of the container. By having a bore seal that extends well down the inside surface of the end portion of the container, the prospect of loss of seal due to differential shrinkage of the closure and the container during the hot fill process is minimised.
In aseptic packaging, the container is sterilised and filled with a sterile food product within the confines of a hygienic environment. The liquid food or beverage is sterilised outside the container using an ultra-high temperature process that rapidly heats, then cools the product before filling the container. Any packaging used in the aseptic process must be able to preserve the sterilisation of the package""s contents until the package is opened by the end consumer. One form of aseptic packaging container presently used is a box-shaped package that is a laminate of paperboard, polyethylene and aluminium.
Certain linerless closures have been proposed for use in sealing containers for carbonated beverages. U.S. Pat. No. 5,423,444 discloses a plastic closure for a container having an externally screw threaded neck, the closure including a top portion and an internally threaded skirt. The closure has an annular sealing rib which projects downwardly from the underside of the top portion. The rib includes a first substantially cylindrical portion contiguous with the underside of the top portion and lying adjacent to or abutting with the skirt, and a second, frusto-conical, portion contiguous with the end of the first portion distal to the underside of the top portion and extending radially inwardly to a circular free edge. During threaded attachment of the closure with the neck, the second, frusto-conical, portion will be engaged by a free end of the neck and folded back towards the first, substantially cylindrical portion of the rib to form a gas tight seal between at least the outer surface of the neck of the container and the closure.
U.S. Pat. No. 5,609,263 discloses a variant of the above closure in which there is at the free end of the second portion of the rib a thick seal ring of substantially circular cross-sectional shape. The rib and the seal ring are dimensioned to engage the free end of the neck when the closure is threaded onto the neck such that when the neck is fully screwed into the closure its free end crushes the seal ring directly against the inside surface of the top portion of the closure.
Australian Patent Application No 80944/98 discloses still further variants of the closure described in U.S. Pat. No. 5,423,444. In one variant, the sealing rib of the closure has a third portion connected to the second portion at or adjacent its circular edge and extending generally in a direction away from the top portion. The third portion is substantially no thicker than the second portion and has a length longer than its thickness. On attachment of this closure to a container, the third portion is positioned between the neck of the container and the underside of the top portion of the closure.
The present invention is directed to a sealing rib arrangement for closures that further improves the sealing ability of linerless closures of the type identified in the abovemenitioned prior art particularly when used in the hot fill process.
According to a first aspect, the present invention relates to a closure suitable for mounting onto a container, the container having an opening defined by an end portion of the container, the closure including a top portion and a skirt portion depending from the top portion, an annular sealing rib projecting downwardly from an underside of the top portion, the rib including a first portion which is contiguous with the top portion and having an inner surface, which inner surface lies radially inwardly of the skirt portion and at least a second, frusto-conical, portion contiguous with the first portion and separated from the top portion by the inner surface of the first portion, the second portion having an upper side and an underside and extending radially inwardly to a circular edge, the inner surface of the first portion having an internal diameter relative to the external diameter of the end portion of the container to which the closure is to be attached such that during attachment of the closure with the end portion of the container, the sealing rib will be engaged by said end portion of the container so folding the second portion at least towards the inner surface of the first portion of the rib to form a seal between at least an outer surface of the end portion of the container and the closure, the closure being characterized in that there is an annular protrusion formed on the underside of the second portion and extending outwardly therefrom, the protrusion on attachment of the closure with the end portion engages the outer surface of the end portion so causing the sealing rib to be disposed over a greater area of the outer surface of the end portion of the container.
In a preferred embodiment, the annular protrusion comprises an annular ridge extending outwardly to a peak. The ridge is preferably substantially triangular in cross-section. One surface of the ridge preferably comprises an end portion engaging surface that acts to extend the area of the seal between the second portion and the container end portion on attachment of the closure to the container. The annular protrusion can be positioned about midway between the first portion and the circular edge of the second portion. In another embodiment, the annular protrusion can be positioned closer to the first position than the circular free edge of the second portion.
In one embodiment, the annular protrusion can have a resiliently flexible member extending outwardly from or adjacent the peak of the annular ridge. The flexible member, on attachment of the closure, engages the outer surface of the end portion and is flexed relative to the ridge. The flexing of the flexible member serves to provide further extension of the sealing area between the second portion and the outer surface on attachment of the closure. The resiliently flexible member preferably extends downwardly and inwardly from the peak of the annular protrusion prior to attachment of the closure to the container end portion. Further, the resiliently flexible member can taper in thickness as it extends away from the second portion of the sealing rib.
The end portion of the container to be sealed by the present invention preferably has a free end, an outer, preferably cylindrical, surface and an inner, preferably cylindrical, surface, the inner surface defining a bore. The join between the free end and the inner surface and the join between the free end and the outer surface are each preferably smoothly curved and define respectively what are hereinafter called the inner and outer sealing radii of the end portion of the container. Containers having end portions which do not have an inner and/or an outer sealing radii will, however, also be sealable by the closure defined herein.
The closure is preferably provided with a screw thread on an inside surface of the skirt portion adapted to engage with a corresponding thread on the outer surface of the end portion of the container. It is, however, possible for the container and the closure to be formed with other complementary attachment means. Such an arrangement could, for instance, comprise snap-on attachment means having a rib on the inside surface of the closure and a corresponding groove on the outer surface of the end portion of the container.
The inner surface of the first portion is preferably substantially cylindrical. The first portion of the rib can comprise a thickening of the skirt portion in the region adjacent the skirt""s connection to the top portion. By comprising such a thickening, the root of the second portion of the rib is moved inwardly of the part of the skirt portion having the screw thread or other attachment means.
In another embodiment, the first portion of the sealing rib is formed radially inwardly of the skirt portion with an annular space therebetween. In a still further embodiment, the first portion of the sealing rib can be in abutment with the skirt portion.
In yet a further embodiment, the first portion of the rib can have a thickness that increases as it extends in a direction away from the top portion of the closure. This thickening of the first portion serves to increase the force of the pressure of the rib against the outer surface of the end portion of the container on attachment of the closure to the end portion. The thickness of the first portion can increase at a uniform rate along the length of the first portion away from the top portion, however, it could do so in a non-uniform manner. The increase in the thickness of the first portion means that the inner surface and, where there is one, the outer surface, of the first portion will each not necessarily be exactly cylindrical. They may respectively taper slightly inwardly and outwardly relative to the axis of the closure in a direction away from the top portion of the closure.
The inner surface of the first portion serves to form an abutment towards which the second portion is folded during attachment of the closure with the end portion of a container. Preferably, during attachment, the second portion will be folded back against the first portion such that it bears against the inner surface of the first portion. This will cause the second portion, including the annular protrusion, to bear more strongly against at least the outer surface of the end portion of the container and so form a better seal with at least the outer surface of the end portion.
In a further embodiment, the sealing rib can include a third portion connected to the second portion at or adjacent the circular edge of the second portion and extending generally in a direction away from the top portion. The third portion is preferably substantially no thicker than the second portion and further preferably has a length longer than its thickness. The third portion of the sealing rib is preferably contiguous with the circular edge of the second portion, though it may be spaced slightly radially outwardly from it. The third portion also preferably projects generally axially away from the top portion of the closure to its distal end. The third portion is preferably substantially cylindrical and can have both a cylindrical inner surface and a cylindrical outer surface. The third portion can join the second portion in an angular disjunction or it may join it in a smooth angular transition from the generally radially inward direction of the second portion to a generally axial direction. In this embodiment, on attachment of the closure to the end portion of the container, the third portion preferably seals with the end portion from a position on the outer surface of the end portion to at least the apex of the free end of the end portion.
The closure according to the present invention may be moulded from any suitable synthetic plastics material, however it is preferred that it is formed from a suitable grade of polyethylene or polypropylene. It is also preferred to form the closure in one piece. The closures could, however, be formed in two or more parts with at least the sealing rib formed separately from the top portion and the skirt portion.
It will be apparent to persons skilled in the art that numerous modifications may be made to the closure described in this specification without departing from the scope of the invention as earlier defined. The closure, for instance, is preferably provided with a tamper evident band adapted to provide an indication of removal or attempted removal of the closure from a container. The tamper evident band can extend from the skirt portion by connection through a plurality of frangible bridges. As the closure is removed from a container, the tamper evident band preferably provides an indication of this removal either before or as the second portion of the sealing rib disengages with at least the outer surface of the end portion of the container. This serves to ensure the integrity of the container""s contents, that may have been filled by a hot fill or aseptic process, until ultimate consumption or use by the consumer of the container""s contents.
As is described in Australian patent specifications 668197. the contents whereof are incorporated herein by reference, the band can also comprise a generally cylindrical body portion and a segmented rib extending inwardly of the body portion and adapted to provide a lip having an inner free edge to engage under a retaining flange extending outwardly from the end portion of the container. The combined length of the segmented ribs can be equal to at least 50% of the internal circumference of the band and the segmented ribs are preferably separated from each other by a gap. Each of the rib segments can each have an upper surface facing generally towards the top portion of the closure and an underside facing generally away from the top portion, with the inner surface of the band having a plurality of radially inward projections extending from above the free edge of the band and not extending beyond the inner free edge of the lip.
As is described in Australian patent specification 683598, the contents whereof are incorporated herein by reference, the upper surface of each rib segment extending inwardly of the body portion can comprise a first surface contiguous with the body portion of the band, which surface slopes inwardly and downwardly away from the top portion, and a second surface which extends radially inwardly from the inner terminus of the first surface and has a slope angle substantially normal to the skirt portion of the closure.
As is described in U.S. Pat. No. 5,676,269. the contents whereof are incorporated herein by reference, the tamper evident band can be joined to the skirt portion of the closure by a plurality of frangible bridges and at least one non-frangible bridge. The band can further have a substantially L-shaped slot extending through the side wall of he band, the horizontal leg of which terminates directly adjacent to or under the non-frangible bridge, and a weakened frangible region extending from the terminating end of the horizontal leg axially downwardly to the bottom of the band distal the frangible bridges.
The underside of the top portion of the closure can also have an engagement means comprising a continuous or segmented annular ridge radially inside of the sealing rib. The upper side of the second portion of the rib may also be formed with a complementary engagement means comprising a continuous or segmented annular ridge as is described in U.S. Pat. No. 5,782,369, the contents whereof are incorporated herein by reference. On attachment of the closure with the end portion, the complementary engagement means on the second portion engage with the underside of the top portion. Where the underside of the top portion has the engagement means, the respective engagement means preferably are adapted to interlock as the closure is attached to the container thereby holding the sealing rib touching the underside of the top portion stationary and causing the second portion of the sealing rib to be disposed over a still greater area of the underside of the top portion as well as the outer surface of the end portion.
Where the closure has a screw thread oil the inner surface of the skirt, the thread can be continuous or formed of a series of thread segments. If formed from a series of thread segments, the thread segments can be arranged, starting from a first thread segment distal to the top, along a helical thread locus, as is described in Australian patent specification 668197. Each of the thread segments except the first can be formed with two substantially planar end surfaces that are inclined to the axis of the closure and face away from the top of the closure, that is they face in the direction that a mould core used to mould the closure was withdrawn. In this specification, the term xe2x80x9csubstantially planar surfacexe2x80x9d is used to describe a surface that is nearly actually planar or that is curved provided that it all faces in the defined direction. The first of the thread segments is preferably pointed at its end distal to its one adjacent thread segment to assist in mating the thread on the closure with a complementary thread on the neck of a container.
The substantially planar ends of the thread segments can also be inclined to a notional radial plane of the closure extending from the longitudinal axis of the closure to the end of the respective thread segment such that the ends are inclined to the cylindrical skirt by an angle that is less than the angle that the respective notional plane makes with that skirt.
There also can be at the line of meeting of the first and second portions of the sealing rib, a weakened zone or annular region of weakness to assist even deformation of the second portion relative to the first as the closure is attached to a container as is described in Australian patent specification 637706, the contents whereof are incorporated herein by reference.
In a further aspect, the present invention comprises a mould for forming a closure as defined herein. The mould can be used to form the closure using injection or rotary moulding. It will be appreciated by persons skilled in the art that other suitable techniques for forming the closure could also be utilised.
In another aspect, the present invention comprises a container having an opening defined by an end portion of the container, the end portion being sealed by a closure as defined herein. The container can be used in an aseptic or hot fill process.
In a still further aspect, the present invention comprises a method of forming a closure as defined herein, the method comprising the step of moulding a synthetic plastics material in a mould.
The method can comprise the step of injection moulding the synthetic plastics materials in the mould.
In yet a further aspect, the present invention comprises a method of applying a closure as defined herein to an end portion of a container, the method comprising the step of turning the closure onto the end portion of the container until the closure seals the container.